Thermal insulation gel with controlled crosslinking for petroleum hydrocarbon transmission lines

ABSTRACT

The present invention relates to and uses, in order to prevent crude oil from “congealing” in a transportation line, a controlled-crosslinking thermal insulation gel, i.e. relatively fluid at the start and developing in-situ gelation in lines only under certain conditions, temperature conditions among other things. In order to obtain controlled crosslinking, it is possible to carry out 1) Physical crosslinkings, i.e. physical bonds between polymers—completely reversible bonds by thermal effect and/or mechanical shear—and 2) Chemical crosslinkings: monomers or polymers having functions allowing chemical bonds to be established between polymers.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the technical field of thermalinsulation of oil transportation lines whose operating conditions inproduction wells are of the order of 60 to 120° C. as regardstemperature and about 300 bars as regards pressure; the crude oil isthen liquid and pumpable. The pressure and the temperature fallcontinuously along these lines and congealing of the crude oil is themajor drawback.

The application relates more particularly to offshore as well as onshoredrilling where the temperatures are very low or even negative.

TECHNICAL PROBLEM

In offshore development, the production well is provided with aproduction wellhead that rests on the sea bottom. The crude oil then hasto be carried to tankers, storage barges or storage and/or pumpingplatforms, by means of complex systems of risers, pipelines and similarmeans, referred to hereafter as lines or flowlines.

Under deep and very deep offshore drilling conditions, the environmentof the risers is water at 0-10° C., the pressure decreases and the crudetherefore congeals because of the deposition of hydrates, paraffin,

black mud

, etc.

These lines can be about twenty km long and, in case of production stopdue to congealing of the crude, the maintenance and servicing operationsare extremely expensive. Congealing of the crude oil therefore has to beprevented in particular.

Current Solutions:

-   -   Heating of the lines by means of hot water or resistors    -   Thermal insulation of the lines with insulating material sheaths        such as glass wool, rock wool, insulating foam . . .        The drawbacks are:    -   difficult to implement 1)    -   efficiency loss in case of breakage and in the presence of water        2)    -   high cost 3)    -   Pipe in pipe        technique (concentric lines) with the annulus evacuated or        filled with a rare gas (argon, xenon . . . ), which are good        thermal insulants.        Drawbacks: Points 1)+3)    -   Syntactic foam: system where hollow glass marbles are embedded        in a thermosetting resin matrix as described in patent U.S. Pat.        No. 5,575,871 (Takeda Chemical Ind./1999)        Drawbacks: Points 1)+2)+3)    -   Gel based on ethylene glycol and water.

Prior Art:

-   1) U.S. Pat. No. 5,290,768 Merck & Co/1994): Polysaccharide    thickener of Welan™ type in ethylene glycol and with EDTA (ethylene    diamine tetra-acetic acid) as rust complexing agent.-   2) U.S. Pat. No. 5,876,619 (Montsanto/1999): Polysaccharide    thickener of scleroglucane type in glycerin and water.    Drawbacks:    -   sensitive to bacteria pollution    -   sensitive to rust    -   heavy (ballast product).    -   Gel based on petroleum products (gas oil, kerosine, mineral        oils):        1) U.S. Pat. No. 5,177,193 (Ravchem Corp/1993): various polymer        gels in a mineral base with chemical crosslinking        Drawback: Point 1)        2) U.S. Pat. No. 5,858,489 (Elf Aquitaine Production): Aerogels        Drawback: Point 1) extremely difficult to implement        3) U.S. Pat. Nos. 5,871,034 and 60,092,557 (G. R. Summer 1999        and 2000): Mixture of bitumens with thermoplastic polymers and        mineral fillers.        Drawbacks: Point 1) and soft product under high pressure and        high temperature.        4) U.S. Pat. No. 4,941,773 (Smit Offshore Contractors, 1990):        The base and kerosine thickened by thermosetting resins based on        polyols and aldehydes.

Among all these solutions, gels currently represent the mostadvantageous technique as regards its cost, material selectionflexibility and ease of use. They essentially consist of a base and of athickener:

-   -   base: the most thermally insulating possible base is selected,        generally petroleum or chemical products or glycol derivatives    -   thickener: used to congeal the base and thus to prevent thermal        convection phenomena.

General Drawbacks of the Existing Techniques:

Apart from gels, the solutions are immediately solid insulants that aredifficult to use.

The current gels are

pasty

system that are less difficult to use than solid insulants, but theyremain difficult and excluded in lines with complex configurations suchas bundles. These are tubes attached to one another comprising forexample two production tubes and three smaller lines or tubes used tocarry other fluids, the assembly being embedded in a common externalsheath filled with thermally insulating gels.

Many pressure losses occur during filling of these bundles, without itbeing possible to use high-pressure pumping means (>100 bars forexample) because of the low mechanical strength of the outer walls, andair pockets or air bubbles inevitably appear. This can pose problems ofcollapse of the external sheath under high pressure (150 bars) underdeep sea conditions.

SUMMARY OF THE INVENTION

The present invention relates to and uses, in order to prevent the crudeoil from

congealing

in a line, a controlled-crosslinking thermal insulation gel, i.e. arelatively fluid gel in the beginning, gelation occuring in-situ in thelines only under certain conditions, temperature conditions among otherthings. The gels obtained are mechanically and thermally stable at highand low temperature, and especially in very weakly solvent bases such aspure linear paraffins, pure isoparaffins . . . and also especially withbases of the same type exhibiting phase changes such as crystallization.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, controlled crosslinking can be obtained bycarrying out:

-   1) Physical crosslinking: i.e. by establishing physical bonds    between polymers, notably with the following means:-   a) Diblock or triblock sequential polymers: crosslinking nodes by    affinity, then phase segregation-   b) Polymers having functions allowing physical bonds (hydrogen, Van    der Waals, dipole-dipole, etc.), for example polar functions such as    alcohols, acids, amines, ethers, esters . . . and similar functions,    generally functions with heteroatoms of O, N, S, Cl type.-   2) Chemical crosslinking: Monomers or polymers having functions    allowing to achieve chemical bonds between polymers.

The advantages are as follows:

-   -   Ease of use (pumping, setting, complex systems)    -   Homogeneous gel, without        air bubbles or pockets    -   No thermal convection    -   Stable at high temperature between 80-150° C.    -   Great durability    -   Pressure resistant    -   Thermal insulant    -   Light gel (density<0.8)    -   Physical gel: specifications flexibility, i.e. reversible or        irreversible, pseudoplastic or thixotropic    -   Products more economical than syntactic foams.

Chemical systems usable according to the invention: the followinginstances are given by way of non limitative example, and the manskilled in the art can complete them according to his general knowledgeand possibly to some routine tests.

1) Bases:

-   -   petroleum products: light cuts or others, according to the        application considered, such as kerosine, gas oil, cut referred        to as petroleum spirit; type 60 (S or NS) mineral bases up to        paraffins, bitumens and similar products,    -   petroleum products with transformation: linear paraffins or        isoparaffins . . . , hydroisomerized bases, . . . ,    -   chemical derivatives of glycol, of monoethylene glycol,        monopropylene glycol, diethylene glycol and similar types,    -   water→insulants+ballast,    -   vegetable oils such as rapeseed, sunflower, soybean, palm oil,        etc., extracted from seeds, plants, barks, fruit, . . .    -   synthetic bases such as polyalphaolefins (PAO), polyisobutylenes        (PIB), polyalkyleneglycols (PAG), polyinternal olefins (PIO),        fatty esters, fatty alcohols, fatty ethers.

Among these bases, 2 categories can be distinguished:

-   -   (1) the bases, light (of very low viscosity) or not, which do        not crystallize at positive temperatures,    -   (2) the bases that crystallize at positive temperatures.

The latter bases are particularly interesting when this crystallizationis exothermic and when this energy is used to compensate for the heatwaste at low temperature of the sea bottom It is well-known that themore linear and the longer the hydrocarbon chains, the more they tend tocrystallize at increasingly high temperatures. Examples of linearparaffins are Linpar® 13-14, 14, 14-17, 16-18 type paraffins, fattyesters, fatty alcohols, for example Nacol® 12, 14, 16, 18, 20 or 22 . .. Nafol® 12-14, 12-18, 16-18, or simply mineral bases with a highparaffin content.

These phase-change bases form with conventional thickeners often looseand unstable gels when they are subjected to thermal cycles.

2) Physical Gelling Agent:

-   a) Diblock or triblock or radial sequential polymers:

Any diblock or triblock or radial sequential polymer. This veryparticular structure type is mainly obtained by ionic (anionic orcationic) polymerization.

A non-limitative example is the range of products known under thetradename KRATON® and marketed by Shell™. These products aredistinguished by:

-   -   the number of sequences (blocks): two or three or radial    -   an elastomeric sequence of polybutadiene or polyisoprene type,        as it is (D series) or hydrogenated (G series),    -   a sequence of polystyrene type (which forms the crosslinking        phase),    -   the composition (% styrene),    -   the molecular mass,    -   in the case of a triblock or radial polymer, the styrene phases        generally        surround        the elastomeric phase.

The mechanical properties of the gel depend on the nature of the baseused, the grade of the Kraton™ used, the percentage. According to thedesired application, a very

firm

, rubbery, extremely resistant and stable towards thermal or mechanicalstresses, or a very

loose

gel, on the verge of flowing, reversible, thixotropic and pseudoplasticis obtained.

Standard thickeners of polyisoprene, polybutadiene, natural rubber,polyisobutylene, ethylene-propylene copolymers type are alsoadvantageously associated with these physical gelling agents.

Several Kraton™ grades can also be used together according to thedesired performances.

This first category of sequential-structure physical gelling agentswhose crosslinking nodes are the phase segregation zones preferablyinclude, by way of non limitative example, the Kraton® products rangemarketed by Shell™ etc.

The bases preferably used in the following non-limitative examples, asdescribed above, are: a rapeseed methyl ester, a linear paraffin (LinparC₁₀®),

light

cut and

heavy

cut (Linpar C16-C18®), an isoparaffin (Isopar™ M), a standard gas oil,petroleum spirit, etc.

The tests carried out to evaluate the gelation kinetics, the variousmechanical properties, the compatibility of the gel with the base, areas follows:

-   -   A composition is prepared under the conditions mentioned in the        examples hereafter, in a glass bottle provided with a metallic        screw cover to obtain a gel or not.    -   A composition is fluid at the observation temperature if it        flows when the bottle is inclined (or tilted at 180°). In the        opposite case, a gel is obtained.    -   The gel time is the time required for a composition to change        from the fluid state to the state of gel at the temperature of        the experiment.    -   Mechanical strength test: A steel ball of about 10 g is dropped        at a height of about 20 cm above the surface of the gel. The gel        is loose if the ball penetrates the gel with or without bounce.        In the opposite case, the gel is firm, mechanically stable at        the testing temperature.    -   Test intended to evaluate the compatibility and the thermal        stability of the gel with the base under the conditions of a        thermal cycle; the gel is subjected to 2 thermal cycles:        -   (1) Cycle 1: 10 h at 80° C./14 h at 20° C./10 h at 80° C./14            h at 20° C.        -   (2) Cycle 2: 10 h at 80° C./14 h at 0° C./10 h at 80° C./14            h at 0° C.

At the end of the thermal cycle, the gel must remain firm (no mechanicalproperties loss) without

releasing

the base, i.e. existence of 2 phases, a liquid phase and a gel phase.This phenomenon is known as syneresis or bleeding.

This phenomenon is particularly marked in bases with phase changes, forexample Linpar® C₁₈-C₂₀, which crystallizes from 30° C. and which,besides the fact that it is a very bad solvent for conventional polarthickeners, separates from the gel once crystallized.

The physical gelling agents selected according to the invention areperfectly stable with these bases, even bases with

phase change

.

The range of Kraton® thermoplastic polymers finds applications asadditives in adhesives, bitumens, mixtures of thermoplastics, mastics,elastomers, etc.

In the present invention, the Kraton® products described above can bemore or less suitable according to the specific needs and to the basesused. The following examples illustrate this feature in a non limitativeway:

It is also possible to incorporate one or more mineral fillers in orderto optimize the cost of the product, its mechanical or physicalproperties, to weight it or on the contrary to lighten it. The manskilled in the art knows in these fields fillers such as clays,bentonite, barite, calcium carbonates, and examples of lightening agentsare, in particular, glass microballs such as those marketed by the 3M™company, which are microballs of about 10 to 150 microns, with anaverage dimension of about 30 microns, and a double function of productlightening and thermal insulation improvement.

The man skilled in the art will be able to envisage all the fillers andfiller combinations of this type.

EXAMPLE 1 Comparative Test with a Conventional Thickener

-   -   Base=Linear paraffin Linpar® C₁₈-C₂₀    -   Gelling agent=Kraton G 1651 E vs. bentone (Thixogel® VP)    -   Testing temperature=Cycles 1 and 2

The percentages in the examples hereunder are expressed in mass ofactive substance. TABLE 1 Characteristics of the gels Percen- tageKraton ® G 1651 E Thixogel ® VP 4 << Firm >> gel. No bleeding. Fluidsolution Thermal cycle stability 8 << Firm >> gel. No bleeding. Fluidsolution Thermal cycle stability 10 << Loose >> gel. Bleeding. Thermalcycle instability 12 << Loose >> gel. No bleeding. Thermal cyclestability 15 << Firm >> gel. No bleeding. Thermal cycle stability

The example given above clearly shows the advantage afforded by physicalgelling agents in relation to conventional thickeners for a given base,much lower proportion of material used, higher gel quality andstability.

EXAMPLE 2 Manufacturing Process and Direct Use

TABLE 2 Manufacture and use of the products Kraton ® G 1651 Thixogel ®VP Manufac- Dispersion of the powdered Manufacture of a bentone- turepolymer at 40° C. if the base based grease followed by has to be melted,or at ambient crushing, deaeration temperature (20° C.) in the Gelhaving a certain presence or not of other consistency polymers ordispersants Liquid dispersion of << swollen >> polymer powders Use inFilling with the fluid liquid Filling by pumping under the linesdispersion from the bottom pressure (150 bars) and In-situ gelation with<< vacuum draining >> temperature (example: at 80° C. throughout theline gel at 4% gel time = 4 h) or Risk of << air pockets or othersbubbles >>

This example shows the ease and flexibility of use of a physical gelwith in-situ crosslinking and controlled initiation, for example bytemperature.

EXAMPLE 3 Product Conditioning Process in Case of no Direct Use

Temper- Bases ature Composition Aspect Pot life Linpar 20° C. 8% KratonG Heterogeneous 3 to 6 C10 1651 swollen powders months dispersion Linpar20° C. 6% Kraton G Homogeneous 3 to 6 C10 1651 dispersion months 2%Kraton G 1702 Linpar   40° C.(1) 8% Kraton G Heterogeneous 3 to 6 C18-201651 swollen powders months dispersion Linpar   40° C.(1) 6% Kraton GHomogeneous 3 to 6 C18-20 1651 dispersion months 2% Kraton G 1702(1)It is recommended to keep these products or to bring them to atemperature of 40° C. prior to use (crystallization temperature 28° C.).

It appears that, in cases where the product is not directly used fromthe conditioner, incorporation of another polymer allows thehomogeneity, the stability and the pumpability of the product to beimproved.

EXAMPLE 4 Effect of the Base, of the Temperature, of the Nature and ofthe Concentration of the Physical Gelling Agent: Comparative Tests withConventional Polymeric Thickeners

TABLE 3 Formation conditions of a stable gel at 20 or 80° C. Linpar ™Linpar ™ C18-20 C10 Gas oil Isopar ™ M Poly- Fluid Fluid Fluid Fluidisoprene solution solution solution solution any temp. any temp. anytemp. any temp. up to 20% up to 20% up to 20% up to 20% Kraton ™ G 8%firm 8% firm 8% firm 8% firm 1651 gel >= gel >= gel <= gel >= 100° C.80° C. 20° C. 80° C. Kraton G 10% firm Fluid Fluid Not studied 1652 gel<= 20° C. Kraton D 8% loose gel Fluid Fluid Not studied 1111 at 80° C.Kraton D Fluid Fluid Fluid Not studied 1101 Kraton D Fluid Fluid FluidNot studied 1161 Kraton G 8% loose gel 15% loose 8% firm gel Not studied1701 at 80° C. gel at at 20° C. 80° C. Kraton G 8% firm gel 8% loose gel8% firm gel Not studied 1654 at 100° C. at >20° C. at 20° C. Kraton 8%firm 8% firm gel Not studied GRP 6917 gel >= at 80° C. 100° C.

This example shows that, according to the conditions of the application(temperature, base, etc.), the nature of the suitable physical gellingagent and its concentration can be selected.

As described above, these polymers occur as diblocks or triblocks orradial polymer, preferably as triblocks with ethylene-propylenesequences or butadiene or isoprene, preferably ethylene-propylene withstyrene sequences with a styrene composition ranging from 10 to 40%,preferably from 20 to 35%, with weight average molecular weightscharacterized in the manufacturer's data sheet by high, average and low,preferentially high weight average molecular weight. The percentage ofuse of these physical gelling agents depends on the bases used, but itgenerally ranges between 1 and 30%, preferably between 2 and 20%.

EXAMPLE 5 Reversible Gel by Shear and Temperature Effect

Another advantage of these physical gelling agents is that it ispossible to reversibly destroy these crosslinking nodes of thethree-dimensional network which are the styrene phases by temperaturerise and/or mechanical stirring, the latter re-forming as soon as thesetwo effects stop. TABLE 4 Effect of temperature and stirring: perfectreversibility of the gel Heating at 130° C. Heating and stirring with aat 130° C. dispersing device at 2-h rest Initial state for 1 h 1500 rpmfor 1 h at 80° C. Firm gel with 4% Loose gel Fluid Firm and Kraton G1651 in stable gel Linpar C18-20 stable at 80° C.

This reversibility is particularly interesting for use in bundles ofcomplex geometry.

EXAMPLE 6 Characteristics of Physical Gels with Kraton® G 1651 (8%)

TABLE 5 Properties of the gels Linpar C₁₈₋₂₀ Linpar C₁₀ 50° C. 0.7740.755 density 20° C. Thermal convection (1) No No Thermal conduction (2)at 0.16 0.14 80° C. (W · m⁻¹, ⁰K⁻¹)

-   (1) The thermal conductivity is measured at different angles of    rotation; if it is the same everywhere, there is no convection.-   (2) ISO 8894-2    b)    Associative    Polymers:

Certain

associative

polymers give great interactions in certain solvents, which result in athixotropic (variation of the viscosity as a function of time) andpseudoplastic gel.

There is a series of resins which, once dispersed in a solvent, develophighly thixotropic gels. Examples of such resins are ALKYDE, ACRYLIC,URETHANE resins, etc. These resins are extremely complex as regardstheir formula, and their selection and association require a certainexpertise. Without being limitative, the present description will focuson Alkyd resins, which are the most important ones in this application.

-   -   These Alkyd resins result from an addition reaction between a        polyol and a polyacid. They can be long or short in oil,        modified or not, for example with amide, urethane, isocyanate        functions.    -   They are often used in synergy with other resins or polymers of        polyurea, polyamide, polyurethane type, etc.

In relation to the above physical gelling agent family, the latterrather represent a

loose

, thixotropic and pseudoplastic gel. In the first case, gelation isinitiated by the temperature and, in the second case, it occurspractically at the end of the mixing operation and with time.

EXAMPLE 7 Examples of Thixotropic Physical Gels Based on AssociativePolymers

a) Petroleum Spirit Base: Alkyd resin Lixol ™ 27% Resin Super Gelkyd ™391W 30% Dowanol ™ PM 1.5%  Petroleum spirit 41.5%  

b) Linpar C₁₀™ Base:

The petroleum spirit of example a) is replaced by Linpar C₁₀.

c) Gas Oil Base:

The petroleum spirit of example a) is replaced by gas oil.

d) Rapeseed Methyl Ester Base:

The petroleum spirit of example a) is replaced by rapeseed methyl ester.

These gels are prepared according to a protocol determined by eachmanufacturer's expertise.

All these gels are

loose

gels, perfectly thixotropic and pseudoplastic. The ease of use is thesame as for physical gels: the compositions are fluid under heavymechanical stirring (or at a temperature>40° C.) and gelation occurs atrest with time inside the flow lines.

The gels are stable towards the thermal cycles and in time.

The gel based on petroleum spirit was evaluated as regards thermalconvection; no thermal convection and no thermal conductivity could beobserved: λ=0.14 W.m⁻¹, °K⁻¹.

The general compositions of these physical gels based on associativepolymers are between 10-40% alkyd resin, preferably about 35%, possiblywith a polar solvent derived from glycol between 0.5 and 10%, preferably1 to 3%, the rest consisting of the base.

Physical gels are particularly easy to use:

-   -   The polymer(s) are dispersed in the selected base the reaction        does not start.    -   According to the application, the temperature and/or stirring is        used to completely solubilize the macromolecular chains: the        reaction starts.    -   According to products, gelation (congealing) is more or less        fast and occurs with time through physical bonds or segregation        phases.

According to the application requirements, a

loose

, mechanically reversible physical gel may be preferred, i.e. apseudoplastic and thixotropic gel (fluid through shearing), whichbecomes thermally fluid (fluid through temperature increase).

3) Chemical Gelling Agent:

In the case of a chemical gelling agent, two mechanisms can beconsidered:

-   a) the initial mixture is a mixture of reactive monomers which,    under the effect of radical initiators or not, will initiate the    polymerization (or polyaddition) or crosslinking (polyfunctional    monomers) reaction in the presence or not of catalysts, under    predetermined temperature and stirring conditions.-   b) the initial mixture is a mixture of polymers having reactive    functions that react with each other or by means of a monofunctional    or polyfunctional monomer. The latter plays the same crosslinking    agent role as in the first case. This reaction can also start with    radical initiators or not, in the presence or not of catalysts and    under predetermined temperature and stirring conditions.

In the first case, the following non limitative examples can bementioned:

-   -   polymerization (radical crosslinking): the monomers have an        unsaturated bond (double bond) which, under the effect of a        radical initiator, will start the reaction. Examples of monomers        are alkyl methacrylate or alkyl acrylate monomers, vinyl esters,        vinyl chlorides, etc.; examples of polyfunctional monomers are a        neopentylglycol dimethacrylate or divinylbenzene; examples of        radical initiators are peroxides (for example benzoyl peroxide)        or diazoic compounds (for example AIBN:        2,2′azobisisobutyronitrile);    -   polyaddition (or polycondensation) reaction: polyurethanes (the        polyols reacting with the polyisocyanates), polyureas (the        polyamines reacting with the polyisocyanates), polyesters (the        polyacids with the polyalcohols), polyamides (the polyamines        with the polyacids), thermosetting resins of epoxy resin type,        polyimides, etc.

The reactive monomers and the compounds necessary to the reaction aremixed in the selected base and the crosslinking polymerization reactionis generally initiated by a temperature increase. The gel time must becontrolled according to the implementation process.

In the second case, the following non limitative examples can bementioned:

-   -   polymers soluble in the selected base having reaction functions        or double bonds capable of crosslinking the polymers with each        other. Examples thereof are polyisoprenes, hydrogenated or not,        polybutadienes, hydrogenated or not, ethylene-propylene-diene        monomers (EPDM), styrene-butadiene rubbers (SBR), functionalized        polyisobutylenes (with an anhydride, carboxylic or amine        function for example), and more preferably esters referred to as        alkyd resins, resulting for example from an addition between a        polyol and unsaturated fatty acids.    -   In the case of radical crosslinking, initiators such as peroxide        type initiators, for example benzoyl peroxide, etc., or        nitrogen-containing, for example 2,2′azobisisobutyronitrile,        with or without difunctional monomers of neopentylglycol        dimethacrylate or divinylbenzene type are suitable.

The gel time must also be controlled according to the processrequirements.

EXAMPLE 8 Chemical Gel

Alkyd resin Lixol 20% Synolac 6883 20% Coporob 2526 20% BYK 411  1%Monomers and crosslinking agents  2% Radical initiators  1% Catalysts0.8%  Linpar C10 35.2%  

The composition gives a firm gel after about 4 h at 80° C.

The example is given only by way of illustration of the concept ofchemical gel in this application.

The advantages that all these chemical systems of the invention have incommon are:

-   -   a compound that can be fluid to relatively viscous, but        perfectly pumpable and posing no filling problems in lines of        complex geometry and configuration such as bundles, or air        pocket or aeration problems if the compound is too        consistent        ,    -   gelation of the system starts either very progressively in time,        or it is initiated by an external factor (temperature, energy        supply),    -   the gel is thermally perfectly stable from 0° C. to 100° C.,        resistant to biological pollution and stable in time,    -   according to needs, the gel is perfectly compact, supple and        pressure-resistant,    -   for certain bases with crystallization between 0 and 50° C., the        gel remains always stable towards thermal cycles between 0 and        1100° C.,    -   the gels are totally incompatible with sea water, they cannot        fade        , with a density <or =0.8 and therefore relatively easy to        recover in case of an accident. Under certain conditions, these        gels can be non toxic to the marine environment and to man        (vegetable oils, esters, 100% linear paraffin or isoparaffin        base).

Validation of the Application

1.1 Description of the Measuring Model:

(the measuring model is shown in the accompanying sole FIGURE)

The models consist of a 27-mm diameter and 50-cm long steel hub (M)(L>>d so as to limit edge effects) filled with oil maintained atconstant temperature by a direct current-fed heater band.

This steel tube is arranged in a 100-mm diameter Plexiglas™ tube (1) andkept in position by means of polystyrene insulating centering plugs (2).The cavity (3) thus formed is filled with INSULATING GEL in the mosthomogeneous way possible. Heating resistors (4) are arranged in thecentre.

The assembly is immersed in a container comprising water maintained at30° C. by an immersion heater.

The models are equipped with 6 thermocouples T:

-   -   1 on the steel wall    -   1 on the Plexiglas™ wall,    -   4 in the paraffin layer at various depths.

They all have the same angular position.

The object of the measurement is:

-   -   to check the absence of thermal convection by measuring the        temperature field which must remain constant in the three        different angular positions 0, 90 and 1800,    -   to have an average thermal conductivity of the insulant.

This model was filled with a gel based on conventional bentonite inLinpar C18-20 in comparison with a loose gel based on associativepolymers:

In the first case, a particular assembly is used:

-   -   Conditioner heated and stirred at 80° C./1 h. Placed under        vacuum for        dearation        purposes.    -   Device connecting the conditioner to the model with vacuum        downstream and pressure upstream from the conditioner, with a        feed pump to prevent air pockets or bubbles.

In the second case, it is sufficient to mechanically shear the gel basedon petroleum spirit which becomes fluid, to feed the model, to placeunder vacuum for dearation and to let the gel recover its consistency atambient temperature after about 4 hours.

The results obtained are as follows: Gel: 15% Bentone in Gel: petroleumLinpar C18-20 (Ex. 1) spirit (Ex. 6) Thermal loss (W/°K*m2) 8.19 9.01Thermal field Constant Constant At different angles (<1/10°) (<1/10°)Thermal conductivity 0.174 0.147/0.141/0.134 (W/m*°K)

It can be seen that these are very good thermal insulants where thermalconvection phenomena are entirely blocked even in the case of loose gelsin petroleum spirit.

1. A product intended to prevent petroleum hydrocarbons from congealingin lines, production wells and crude transportation lines, notably underoffshore but also onshore production conditions where the operatingtemperatures are low, notably with simple lines or bundlesconfigurations, characterized in that it consists of acontrolled-crosslinking thermal insulation gel that is relatively fluidin the beginning, in-situ gelation occuring only under certaintemperature and energy supply conditions and pumping conditions in saidline.
 2. A product as claimed in claim 1, characterized in that thethermal insulation gel is compatible and mechanically and thermallystable from 0 to 150° C. with poor solvent bases such as linearparaffins or isoparaffins exhibiting crystallization phenomena or not.3. A product as claimed in claim 1, characterized in that, in order toobtain controlled crosslinking, the product is crosslinked by physicalbonds between polymers.
 4. A product as claimed in claim 1,characterized in that it comprises, for the preparation thereof, agelling agent and at least one base selected from the group consistingof petroleum products, petroleum products with transformation, chemicalderivatives of glycols, water→based insulants+ballast, vegetable oilsand synthetic bases.
 5. A product as claimed in claim 4, characterizedin that said bases are selected from the following two categories thegroup consisting of light bases of very low viscosity which do notcrystallize at positive temperatures and bases that crystallize atpositive temperatures.
 6. A product as claimed in claim 4, characterizedin that the gelling agent is a physical gelling agent comprising one ormore diblock or triblock or radial sequential polymers.
 7. (cancelled)8. A product as claimed in claim 6, characterized in that the productfurther comprises polyisoprene, polybutadiene, natural rubber,polyisobutylene, or ethylene-propylene copolymers as thickenersassociated with the physical gelling agents.
 9. A product as claimed inclaim 6, characterized in that further physical gelling agents areassociated with the physical gelling agents in order to improve thehomogeneity, stability and pumpability of the product in cases wherethere is no direct use of the product.
 10. A product as claimed claim 4,characterized in that the base is selected from the group consisting ofa rapeseed methyl ester, a linear paraffin, an isoparaffin, a standardgas oil, and petroleum spirit.
 11. A product as claimed in claim 6,characterized in that said gelling agent is a triblock sequentialpolymer with ethylene-propylene sequences and styrene sequences with astyrene composition ranging from 10 to 40%.
 12. A product as claimed inclaim 11, characterized in that the percentage of use of physicalgelling agents ranges between 1 and 30%.
 13. A product as claimed inclaims 4, characterized in that it the gelling agent comprisesassociative polymers that interact in certain solvents and form athixotropic and pseudoplastic gel.
 14. A product as claimed in claim 13,characterized in that said resins are used in synergy with other resinsor polyurea, polyamide, polyurethane type polymers.
 15. A product asclaimed in claim 1, characterized in that the product comprises aninitial mixture of reactive monomers which will the undergo apolymerization polyaddition, polycondensation or crosslinking reactionunder predetermined temperature and stirring conditions.
 16. A productas claimed in claim 15, characterized in that said reaction is apolymerization reaction and the reactive monomers have an unsaturatedbond double bond.
 17. A product as claimed in claim 15, characterized inthat said reaction is a polyaddition or polycondensation reaction.
 18. Aproduct as claimed in claim 29, characterized in that the initialmixture is a mixture of polymers having reactive functions which willreact with each other or by means of a monofunctional or polyfunctionalmonomer under predetermined temperature and stirring conditions.
 19. Aproduct as claimed in claim 18, characterized in that the polymers aresoluble in the selected base and exhibit reaction functions or doublebonds capable of crosslinking the polymers together, the polymers beingselected from the group consisting of polyisoprenes, hydrogenated ornot, polybutadienes, hydrogenated or not, ethylene-propylene-dienemonomers (EPDM), styrene-butadiene rubbers (SBR), functionalizedpolyisobutylenes (with an anhydride, carboxylic or amine function andalkyd resins.
 20. A process intended to prevent crude oil fromcongealing in a line, in production wells and in petroleum hydrocarbontransportation lines, notably under offshore but also onshore productionconditions where the operating temperatures are very low, notably withsimple lines or bundles configurations, comprising injecting a gel typeproduct as claimed in claim 1 in the fluid state around said line orbetween said line and an external sheath, and inducing in-situ gelationby modification of the temperature, energy supply and pumping rateconditions, and/or of the conditions of initiation of the crosslinkingreaction.
 21. A process as claimed in claim 20, characterized in thatthe gel type product is prepared by dispersing polymer(s) a base underconditions that reaction of the polymer(s) does not start and in thatinducing in-situ gelation is done by controlling temperature and/orstirring to completely solubilizee macromolecular chains and start thereaction so that gelation occurs with time through physical bonds orsegregation phases.
 22. A process as claimed in claim 21, characterizedin that, the gel type product comprises a loose, mechanically reversiblephysical gel which is fluid through shearing and/or thermally fluid whenused, and of which congealing occurs in-situ in the lines.
 23. A processas claimed in claim 20, characterized in that, the gel type product isprepared by mixing of initial reactive monomers which will undergo apolymerization, polyaddition or crosslinking reaction underpredetermined temperature and stirring conditions.
 24. A process asclaimed in claim 23, characterized in that step of in-situ gelationcomprises carrying out a polymerization reaction of the initial reactivemonomers under the effect of a radical initiator, the monomer beingselected from the group consisting of alkyl methacrylate monomers, alkylacrylate monomers, vinyl esters, vinyl chlorides, neopentylglycoldimethacrylate and divinylbenzene and the radical initiators peroxidesneopentylglycol or diazoic compounds.
 25. A process as claimed in claim23, characterized in that the step of in-situ gelation comprisesinitiating a polyaddition or polycondensation reaction by a temperatureincrease.
 26. A product as claimed in claim 1, characterized in that theproduct further comprises one or more mineral fillers selected from thegroup consisting of clays, bentonite, barite, calcium carbonates, andglass microballs
 27. A product as claimed in claim 3, characterized inthat the physical crosslinking bonds are obtained by formingcrosslinking nodes by phase segregation with diblock or triblock orradial sequential polymers.
 28. A product as claimed in claim 3,characterized in that the polymers have functions that allow hydrogen,Van der Waals or dipole-dipole bonds.
 29. A product as claimed in claim1, characterized in that the product is crosslinked by chemical bondsbetween an initial mixture of monomers or polymers.
 30. A product asclaimed in claim 4, characterized in that the base is selected from thegroup consisting of kerosene, gas oil, petroleum spirit, type 60 (S orNS) mineral bases up to paraffins, bitumens, linear paraffins,isoparaffins, hydroisomerized bases, derivatives of glycol, derivativesof monoethylene glycol, derivatives of monopropylene glycol, derivativesof diethylene glycol, water based insulants and ballast, rapeseed oil,sunflower oil, soybean oil, palm oil, polyalphaolefins,polyisobutylenes, polyalkyleneglycols, polyinternal olefins, fattyesters, fatty alcohols and fatty ethers.
 31. A product as claimed inclaim 5, wherein said bases are bases that crystallize at positivetemperatures and are selected from the group consisting of linearparaffins, fatty esters and fatty alcohols.
 32. A product as claimed inclaim 12, characterized in that the percentage of use of physicalgelling agents ranges between 2 and 20%.
 33. A product as claimed inclaim 13, characterized in that the associative polymers are selectedfrom the group consisting of alkyl resins, acrylic resins and urethaneresins.
 34. A product as claimed in claim 33, characterized in that theassociative polymers comprise alkyd resins resulting from an additionreaction between a polyol and polyacid.
 35. A product as claimed inclaim 16, characterized in that the monomers are selected from the groupconsisting of alkyl methacrylate, alkyl acrylate, vinyl esters, vinylchlorides, neopentylglycol dimethacrylate and divinylbenzene.
 36. Aproduct as claimed in claim 35, characterized in that the productfurther comprises a radical initiator selected from the group consistingof peroxides and diazoic compounds.
 37. A product as claimed in claim19, characterized in that the initial mixture further comprises aninitiator.
 38. A product as claimed in claim 19, characterized in thatthe initiator is selected from the group consisting of benzoyl peroxide,2,2′ azobisisbutyronitrile.
 39. A product as claimed in claim 38,characterized in that the initiator further comprises difunctionalmonomers of neopentylglycol dimethacrylate or divinylbenzene.
 40. Aproduct as claimed in claim 26, characterized in that the mineral fillercomprises glass microballs having a diameter of 10 to 150 microns.